1. Field of the Invention
The present invention generally relates to communication systems, and more particularly to a call admission in a mobile communication system.
2. Background of the Related Art
FIG. 1 shows a related-art mobile communication system, comprising a mobile station 10, a base station 20, and a control station 30. The base station comprises a radio frequency (RF) unit 21, a modem unit 22, and a base station processor 23. The RF unit 21 performs an RF transmission function, transmission path check function, and transmission filter function. The modem unit 22 processes CDMA (Code Division Multiple Access) digital base band signals. And, the base station processor 23 serves as the main processor within the base station, performing the function of conducting initialization of the base station, a call process function, and the function of assigning and releasing network and radio resources.
In the related-art mobile communication system described above, users require similar levels of quality of service (QoS) mainly for voice services. Accordingly, the requested amount of network and radio resources would be similar and thus the QoS of most users could be satisfied. Therefore, the call admission control function has been conducted simply based upon the existence of available resources.
The above-mentioned call admission control function means the function of limiting the number of admitted users upon considering the condition of almost all the resources required for performing call connection such as network, radio capacity, modem, power, etc. By conducting call admission control, the QoS of users who have already been active in the base station can be ensured and voice calls that newly arise can be accommodated to the maximum level.
However, as technology progressed, the QoS required by voice users and data users became different in a mobile communication system that simultaneously provides services for voice calls and data calls, and thus frequently there are occasions where the QoS of certain users cannot be satisfied. For example, if there are connections for a large number of data calls, for which comparatively a large amount of network and radio resources are required and the required amount changes frequently, voice calls which should be primarily served would often be rejected in such a mobile communication system.
Further, if a number of voice calls are assigned to a specific frequency assignment (FA), call reject may occur for data calls in the corresponding frequency in such a mobile communication system. Here, call reject means the rejection of an attempt for a call connection for various reasons. In most cases, call reject occurs due to radio problems or failure in processing calls or assigning resources within the system.
In short, where there were only voice calls in the mobile communication system of the related art, no particularly detailed call admission control function was required because the QoS of one voice call was same as the QoS of other voice calls. In contrast, in a mobile communication system which accommodates voice calls and data calls at the same time, a more detailed call admission control function is required.
In mobile communication systems of the related art that accommodate voice calls and data calls at the same time, call admission control has not been conducted actively with regard to voice calls or data calls. Further, the priority of voice calls over data calls has not been taken into consideration. Thus, if a number of data calls were made for a specific sector/FA and if there is no sufficient resource to be assigned for a voice call, the voice call cannot be connected and further no new data calls can be connected.
Moreover, for data calls having some unique features, the simple call admission control function provided by the related art would complicate or make it difficult to implement the process of satisfying QoS demanded by users. More specifically, because QoS of data calls would be different depending on the type of required services, radio and network resource demand would be different accordingly. This complicates the call admission control process.